Molding apparatus for manufacturing panels

ABSTRACT

A mold apparatus and method for manufacturing panels having, as desired, one or more areas of reduced material comprising a facing sheet and integrally attached cell forming walls extending in roughly perpendicular fashion from the facing sheet. Additionally, a method for molding panels, including large scale panels, from thermoplastic resins and other moldable materials requiring significantly less energy than other known molding methods, and providing for panels having one or more areas exhibiting continuous outer surfaces on all dimensions. A lower negative mold member has a plurality of upwardly facing positive standoffs defining interstitial channels into which thermoplastic resin or other moldable material is filled. A generally planar upper mold member is placed on the lower mold, and the combined mold assembly is then subjected to elevated heat and pressure, allowing said thermoplastic resin or other moldable material to melt within the interstitial spaces of the lower mold member. After cooling, upper and lower mold members are separated, and a molded panel structure is removed therefrom.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] (Not applicable)

STATEMENTS AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY-SPONSOREDRESEARCH AND DEVELOPMENT

[0002] (Not applicable)

BACKGROUND OF THE INVENTION

[0003] 1. Field of the Invention

[0004] The present invention relates generally to a mold apparatus andmethod for manufacturing panels. More particularly, this inventionrelates to a method for manufacturing panels having, as desired, one ormore areas of reduced material comprising a facing sheet and cellforming walls extending in roughly perpendicular fashion from saidfacing sheet, wherein said cell forming walls are integrally formed withand attached to said facing sheet. More particularly still, the presentinvention relates to a method of molding panels from thermoplasticresins and other moldable materials which requires significantly lessenergy than other known molding methods. More particularly still, thepresent invention relates to a method of molding panels fromthermoplastic resins and other moldable materials wherein said panelshave one or more sections which exhibit characteristics of a solidpanel, that is, portions of said panels which have roughly continuousouter surfaces.

[0005] 2. Description of Related Art

[0006] Panels constructed of various materials, and embodying manydifferent sizes and shapes, have been known in the art and used in amultitude of applications for some time. Although such applications aretoo numerous to name, some examples include the use of large-scalepanels made of wood, gypsum, metal and/or fiberglass in connection withthe construction of buildings and other structures. Additionally, panelsof various sizes have routinely been used, individually and incombination with one another, as load-bearing elements.

[0007] In most applications, it is beneficial for panels to exhibitdesirable strength characteristics, while remaining relatively light. Inthis regard, attempts have been made to utilize thermoplastic resins andother synthetic materials to replace materials like metal, wood andconcrete to construct such panels. However, to date, it has beendifficult to manufacture panels from thermoplastic resins and othermoldable materials having the desired strength and weightcharacteristics in a cost effective manner. This is particularly true inthe case of large-size panels.

[0008] While it may be beneficial to manufacture solid panels, it isgenerally known that use of cellular structure in panels can greatlyreduce material requirements while maintaining, or in some casesactually increasing, strength characteristics of said panels. In mostinstances, such material reduction results in significant cost savings.In the case of panels molded from thermoplastic resins and othermoldable synthetic materials, the use of cellular structure to reducematerial requirements can have a dramatic effect on the ultimate cost ofsuch molded panels.

[0009] Panels exhibiting cellular structure, in general, and hexagonalshapes or honeycombs, in particular, have been known in the art for sometime. Similarly, molding apparatuses and methods of manufacturing panelscontaining cellular structure are also generally well known in the art.

[0010] U.S. Pat. No. 2,892,339 to Flower et al, discloses panels havingopen faced cellular structure which are constructed of gypsum plaster orother moldable composition, as well as a method of manufacturing same.The panels described in the '339 patent include at least one facingsheet having integral and homogenous cell forming walls disposed withtheir axes at a right-angle to said facing sheet. The '339 patentfurther describes a method of manufacturing such panels comprising afacing-mold table for containing a volume of plaster or other moldablematerial, a series of deformable plugs or offsets for molding cellwalling in one with a facing layer of plaster or other moldablematerial, a vertically movable framing on which such plugs are mountedin spaced relation, means for immersing said plugs in plaster or othermoldable material of the facing-mold to form the whole of the cellwalling for a panel simultaneously with the facing, and means forcontracting the plugs for their withdrawal from the plastic or othermoldable material.

[0011] U.S. Pat. No. 3,509,005 to Hartig discloses a method of applyingmolten thermoplastic resin into a pattern disposed on the surface of arotating roll to form a web of ribs integrally molded to a continuousfilm.

[0012] U.S. Pat. No. 3,617,416 to Kromrey describes a structureconsisting of fiber-reinforced cells, such as honeycombs, which areintegrally molded to a substrate material, as well as a method ofmanufacturing said structure. The method described in the '416 patentutilizes dies formed as continuous individual strips of cells having adesired end configuration. Said die strips are placed side by side andinterfitted to form a mold for a honeycomb structure. Fibers or fabricpre-impregnated with curable resin are wound between the dies to formcellular walls of a honeycomb structure, as well as a substrate layer.The entire structure is then subjected to conditions of elevatedtemperature and pressure to effect a cure.

[0013] U.S. Pat. No. 5,776,582 to Needham discloses loadbearingstructures having interlockable edges. The '582 patent addresses amethod of molding panels having cellular structure out of thermoplasticresins and other materials. The '582 patent briefly describes a pan-likelower mold member into which thermoplastic material and reinforcingfiber is placed. Thereafter, an upper mold remember having positive plugextensions are combined with the lower mold member, and heat andpressure is applied. The positive plug extension is used to deform theresin and reinforcing material to the desired configuration.

[0014] Similarly, U.S. Pat. No. 5,888,612 to Needham, et al, alsodescribes a method of molding panels containing cellular structure. Alower mold member having an ordinary smooth interior surface is firstfilled with thermoplastic material. An upper mold member is configuredwith positive molding dies. Said upper and lower mold members arecombined, and the dies of said upper mold member are used to displacesaid thermoplastic material. Thereafter, the apparatus is subjected toconventional heat and pressure to form the desired panel having cellularstructure.

[0015] One significant problem encountered when molding panels havingcellular structure under the prior art relates to uniform placement ofthermoplastic resin or other moldable material which form cell walls.Under the prior art, thermoplastic resin or other moldable material isloaded into a lower mold member which is typically in the form of a pan.Thereafter, an upper mold member having positive standoffs, spaced apartin a desired pattern, is forced into said lower mold member. In order tocreate the desired cell-forming walls, the thermoplastic resin or othermoldable material must be displaced by said upper mold member in orderto fill voids between said positive standoffs. Unless such resin orother material is uniformly and adequately distributed between saidpositive standoffs, pits or voids will often develop in the cell-formingwalls. Because such thermoplastic resin or other moldable material mustbe mechanically displaced between the positive standoff elements of theupper mold member, the prior art methods of molding have significantlygreater energy requirements than the molding method of the presentinvention disclosed herein.

[0016] Additionally, it is often beneficial to manufacture panels ofthermoplastic resin which have one or more generally solid sections,that is, sections exhibiting roughly the same characteristics as a solidpanel, such as continuous outer surfaces. However, with existing moldingmethods described in the prior art, it is generally not possible to moldlarge-size panels or other items having one or more portions of solidthermoplastic resin, particularly when said solid portions are situatedimmediately adjacent to one or more sections exhibiting cellularstructure. Because a solid mass of thermoplastic material will generallytake a relatively long period of time to completely cool, warping andstress cracking problems can often develop in such parts. In the case ofa molded panel or other item having a solid section of thermoplasticmaterial situated immediately adjacent to one or more sectionsexhibiting cellular structure, a significant difference in mass existsbetween said solid section and the cell walls of the adjacent cellularstructure. As such, a significant cooling differential can exist betweensaid solid sections and said cell walls, which can in turn lead tosignificant warpage and stress cracking problems in such a molded panel.

[0017] Accordingly, there is a need for a method for manufacturingpanels from thermoplastic resins and other moldable materials whereinsaid panels exhibit a facing sheet and roughly perpendicular cellforming walls extending from said facing sheet in order to define one ormore open-faced cells, and wherein said cell forming walls areintegrally formed with said facing sheet. Moreover, there is a need fora method of molding panels from thermoplastic resins and other moldablematerials which yields uniform and consistent cell forming walls,requires significantly less energy than currently available moldingmethods, and which further permits molding of panels having one or moresections exhibiting characteristics of a solid panel, such as continuousouter surfaces.

SUMMARY OF THE INVENTION

[0018] In accordance with the present invention, a molding apparatus anda method for manufacturing panels from thermoplastic resins or othermoldable materials is provided. Although the apparatus and methoddescribed herein can be used to manufacture panels of many differentsizes and shapes, it must be noted that the present invention permitsmanufacture of both small and large-scale panels. Further, the method ofmanufacturing panels described herein requires significantly less energythan other known molding methods, and permits molding of panels whichare significantly larger than panels which can be molded under otherknown molding methods.

[0019] Furthermore, in accordance with the present invention, there isprovided herein a method of manufacturing panels having one or moreareas of reduced material. Said areas of reduced material are generallyin the form of cellular structure comprising a facing sheet and cellforming walls extending in roughly perpendicular fashion from saidfacing sheet, and wherein said cell forming walls are integral with saidfacing sheet. Although said cell forming walls, and thus said cellularstructure itself, can be configured in any number of shapes and sizes,the cellular structure is preferably in the form of a hexagonalhoneycomb structure to maximize strength characteristics of a panel.

[0020] It is frequently advantageous for molded panels to include, inaddition to one or more areas defining cellular structure, one or moreareas having continuous (that is, non-cellular) outer surfaces. Themethod of manufacturing panels described herein permits the molding ofsaid panels from thermoplastic resins or other moldable materials withportions thereof alternatively exhibiting cellular structure, orcontinuous outer surfaces. Further, the method of manufacturingdescribed herein allows for great flexibility with respect to theconfiguration of said cellular structure and continuous outer surfaces,while alleviating warping and stress cracking problems commonlyassociated with conventional molding methods.

[0021] In contrast to the prior art, in which shallow pans are filledwith thermoplastic resin or other moldable material, either in liquid orsolid form, and a positive upper mold is used to displace such resin toform cell walls, the present invention utilizes a lower negative moldmember which is initially filled with resin or other moldable material.The lower negative mold has a plurality of upwardly facing positivestandoffs defining interstitial channels into which thermoplastic resinor other moldable material is filled. Said interstitial channels can beused to define any number of cellular structures; however, in thepreferred embodiment said channels form an interconnected honeycombpattern. Once the lower negative mold has been charged with resin asdesired, a generally planar upper mold member is placed on the lowermold. The combined mold assembly is then subjected to elevated heat andpressure, allowing said thermoplastic resin or other moldable materialto melt within the interstitial spaces of said lower mold member. Aftercooling, upper and lower mold members are separated, and a molded panelstructure is removed therefrom.

[0022] Generally, it is beneficial to manufacture panels having cellularstructure, as well as a facing sheet integrally attached to the cellforming walls of said cellular structure. Such a panel is formed byfilling the interstitial spaces or channels between standoffs of a lowermold member with thermoplastic resin or other moldable material.Thereafter, a topping layer of such material is placed upon the uppersurface of said standoffs, as well as over said channels of the lowermold member which are already filled with such resin or other moldablematerial. A generally planar upper mold member is then placed on saidlower mold member. In order to accommodate a topping layer ofthermoplastic resin or other moldable material, the lower mold member isequipped with raised outer containing walls along the peripheral edgesof said lower mold member. Further, the positive standoffs of the lowermold member are sized such that the upper surface of said positivestandoffs are recessed lower than said outer containing walls of saidlower mold member. After melting, said topping layer forms a roughlycontinuous facing sheet which is integrally attached to said cell walls,which are themselves formed by the thermoplastic resin or other moldablematerial disposed within the interstitial spaces of said lower moldmember.

[0023] Additionally, the method of molding disclosed herein permits theinclusion of additives into said panels during the molding process.Because a facing sheet defining one side of a panel can be used as asupport surface, it is generally beneficial to increase the frictionalcharacteristics associated with said facing sheet. One way to improvesuch frictional characteristics is to utilize a type of resin or othermoldable material which exhibits different properties than the baseresin or other material used to construct the remainder of the panel.Such an additive is ideally loaded into a lower mold member over a resintopping layer which is used to form a facing sheet for a panel.

[0024] Other additives, besides those which are intended to improvepurely frictional characteristics of the panels, can also be included inpanels manufactured pursuant to the method disclosed herein. By way ofillustration, materials which are used to disperse electrical charges,such as any member of commercially available anti-static additives, canbe loaded into the lower mold member with resin or other moldablematerial and molded into the panels described herein. Moreover, theadditions can also be compounded with thermoplastic resin or othermoldable materials prior to the actual molding process. By introducingadditives into panels through the disclosed molding process, saidadditives can be widely and evenly disbursed throughout said moldedpanels. Alternatively, it may be desirable to load such resins and/oradditives in stages, thereby resulting in layering of such resins and/oradditives which can greatly improve characteristics of molded parts.

[0025] Panels such as those described herein are often used asindividual load bearing elements, or to construct larger load bearingstructures or surfaces. As such, it is often advantageous to mold suchpanels from materials having desired strength and durabilitycharacteristics. In the case of thermoplastic resins, the resins whichexhibit such desired strength and durability characteristics generallyhave higher densities than other similar resins. When melted, such highdensity resins are typically very viscous. It is generally thought thatstructures such as the large-size panels of the type discussed hereincannot be manufactured economically and in large quantities through acompression molding process, because extremely large amounts of energyare required to uniformly distribute such high viscosity resins betweenpositive standoffs of a mold. However, the design of the presentinvention permits uniform distribution of such resin within interstitialspaces between positive standoffs of a lower mold member withoutrequiring excessive amounts of energy.

[0026] The method of manufacture described herein can be utilized tomanufacture panels, or specific portions thereof, exhibiting roughlycontinuous outer surfaces. Such panel portions have roughly the samecharacteristics as solid sections. However, as discussed above, it isoften not feasible to mold such solid sections from thermoplastic resinsor other moldable materials due to warping and stress cracking problemsassociated with differential cooling rates.

[0027] In order to mold panels or portions thereof exhibiting roughlycontinuous outer surfaces, a sacrificial component having open facedcellular structure and an integral facing sheet or skin is firstprepared, preferably pursuant to the molding method disclosed herein.Although said sacrificial component can be molded into a particularshape or configuration as desired, it is also possible to simply cutdown a portion of a larger previously molded panel having cellularstructure to the desired dimensions. The appropriately sized sacrificialcomponent is placed within a pan-like or hollowed out portion of thelower mold member, and covered with thermoplastic resin or othermoldable material. The size and shape of the pan-like or hollowed outportion of the lower mold member will depend on the configuration of thefinished panel which is desired; for example, if an entire panelexhibiting continuous outer surfaces is desired, then the entire lowermold member would be hollowed out. Conversely, if a panel having bothareas of continuous outer surfaces and open faced cellular structure isdesired, then only the portions of the lower mold member whichcorrespond to the generally solid portions of the finished panel wouldbe pan-like or hollowed out. Thereafter, an upper mold member of thepresent invention is installed, and heat and pressure are applied. Thethermoplastic resin or other moldable material encases said sacrificialcomponent, thereby resulting in a molded panel, or portion thereof,having roughly continuous outer surfaces. In the preferred method, thesacrificial component is placed within the lower mold member with theopen cellular structure of said sacrificial component facing upward. Asa result, loading of thermoplastic resin or other moldable material intothe lower mold member will result in such resin or other materialfilling such open cellular structure of said sacrificial component.

[0028] It is possible that thermoplastic resins or other moldablematerials can be introduced into the lower mold member of the presentinvention in a molten state. However, for convenience and ease ofhandling, it is envisioned that said resins or other materials areconveniently added to said lower mold member in solid form as pellets,granules or the like. While said pellets or granules can be of differentsizes, it is generally envisioned that pellets of relatively constantsize and shape are utilized to fill said lower mold member to facilitateuniform distribution therein. Said pellets must be sized to permituniform loading of said lower mold member, in general, and theinterstitial spaces between positive standoffs of the lower mold member,in particular.

[0029] Although the upper and lower mold members can be constructed ofany number of functional materials, said mold members are ideallyfabricated from metal such as aluminum. Because of the configuration ofsaid upper and lower mold members disclosed herein, significantly morematerial is required for a lower mold member than an upper mold memberof the present invention, which results in a significant differential inmass between said mold members. Such a mass differential typically inturn results in a variance in thermal transfer between said upper andlower mold members during the molding process. Such problems can includedifferent growth and shrinkage rates when said mold members are exposedto elevated temperatures and thereafter allowed to cool. In order toalleviate such problems associated with thermal transfer differentials,spacers can be affixed to said upper mold member. Said spacers serve toreduce the surface area in contact between said upper mold member and aheat source, such as a platen or hot press, which is used to elevate thetemperature of the mold members. In the preferred embodiment, saidspacers can be of different sizes and shapes to facilitate flexibilityin configuration of said spacers on said upper mold member.

[0030] The drawings and descriptions of the preferred embodiments setforth herein describe only preferred embodiments of the presentinvention, simply by way of illustration of the best mode contemplatedof carrying out this invention. It must be noted that this invention iscapable of other and different embodiments, and its several details arecapable of modification in various respects, all without departing fromthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031]FIG. 1 is a perspective view of a molded panel in accordance withthe present invention.

[0032]FIG. 2 is a perspective cross sectional view taken substantiallyalong line 2-2 of FIG. 1.

[0033]FIG. 3 is a plan view of a molded panel in accordance with thepresent invention.

[0034]FIG. 4 is cross sectional cut-away view taken substantially alongline 4-4 of FIG. 3.

[0035]FIG. 5 is a plan view of a lower mold member in accordance withthe present invention.

[0036]FIG. 6 is a cross sectional view of a lower mold member takensubstantially along line 6-6 of FIG. 5.

[0037]FIG. 7 is a plan view of an upper mold member in accordance withthe present invention.

[0038]FIG. 8 is a cross sectional view of an upper mold member takensubstantially along line 8-8 of FIG. 7.

[0039]FIG. 9 is an exploded perspective view of sacrificial molded partsin a lower mold member in accordance with the present invention.

[0040]FIG. 10 is a cross sectional view of a lower mold member beingloaded with moldable material in accordance with the present invention.

[0041]FIG. 11 is a cross sectional view of an upper and lower moldmember of the present invention loaded with moldable material.

[0042]FIG. 12 is a partial plan view of the lower surface of an uppermold member of the present invention taken substantially along line12-12 of FIG. 8.

[0043]FIG. 13 is a cross sectional cut-away of an upper mold member ofthe present invention taken substantially along line 13-13 of FIG. 12.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0044] Referring to the drawings, FIG. 1 depicts typical molded panel 10having cellular structure 11. Cellular structure 10 is comprised of aplurality of individual cells 12, defined by interconnected cell formingwalls 13. Because panel 10 can be used as a load bearing element, eitherindividually or in tandem with other such panels, cells 12 are depictedas hexagonal honeycombs for strength characteristics. However, it isenvisioned that said cells can take any number of shapes, as desired,such as circular, oval, rectangular or the like.

[0045]FIG. 2 is a cross sectional view of panel 10 roughly along line2-2 of FIG. 1. Skin layer 14 defines a base for cells 12. The uppersurface of skin layer 14 forms the bottom of individual cells 12, whilethe lower surface of skin layer 14 forms continuous lower surface 15 ofpanel 10. Cell forming walls 13 extend in roughly perpendicular fashionfrom skin layer 14. Skin layer 14 is integrally attached to the base ofsaid cell forming walls 13.

[0046] As will be understood, panels manufactured in accordance with themethod described herein can have any number of configurations. It is notnecessary that such panels be rectangular in shape or limited to foursides. Further, it is not necessary that the cellular structure of saidpanels be limited to a single region of said panels, or that the cellsbe in the shape of hexagonal honeycombs. Nonetheless, in the preferredembodiment, it is envisioned that the panels manufactured in accordancewith the present invention be large-size molded panels, molded fromthermoplastic resin or other moldable material, and having a large areaof reduced material in the form of hexagonal honeycombs. In thepreferred embodiment, the molding apparatus and method of manufacturedescribed herein can be utilized to mold panels which are incorporatedinto large size load-bearing mats which can be used to constructroadways and other temporary work surfaces.

[0047]FIG. 3 depicts a molded panel 30 in the form of a component partof such a large size load-bearing mat. Panel 30 has an area of reducedmaterial in the form of cellular structure 31 which is comprised of aplurality of individual cells 32 defined by interconnected cell formingwalls 33. In the preferred embodiment, individual cells 32 are in thepattern of hexagonal honeycombs. Integral skin 37 is located at the baseof cells 32 and cell forming walls 33 to form a continuous surface alongthe underside of said panel. Areas of increased mass 34 and 35,exhibiting roughly continuous outer surfaces, are located on twoadjacent peripheral edges of panel 30. Although it is envisioned thatsaid areas of increased mass can be solid, that is, comprising a solidcross section of thermoplastic resin or other moldable material, themethod of manufacture described herein provides means for molding saidareas of increased mass without actually molding a completely solidplastic component, thereby eliminating warping and stress crackingproblems generally associated with such areas of solid resin or othermoldable material. Recessed receptacles 39 extend through areas ofincreased mass 34 and 35 of panel 30. Additionally, molded panel 30 hasa plurality of bore holes 36, which extend completely through saidmolded panel 30.

[0048]FIG. 4 depicts a cross sectional cut-away view of panel 30 takensubstantially along line 4-4 of FIG. 3. Panel 30 has area of reducedmaterial in the form of cellular structure 31 comprised of a pluralityof individual cells 32 defined by interconnected cell forming walls 33.Integral skin 37 is located at the base of cells 32 and cell formingwalls 33. Integral skin 37 also forms generally planar surface 38,having a plurality of raised traction promoting elements 38 a situatedthereon. Area of increased mass 34 is located at a peripheral edge ofpanel 30. Recessed receptacles 39 extends through area of increased mass34.

[0049]FIG. 5 depicts a lower mold member 50 in accordance with theinvention described herein. Although such a lower mold member can haveany number of specific configurations, for illustration purposes saidlower mold member is depicted in FIG. 5 as a mold for use in moldingmolded panel 30. Lower mold member 50 has sunken tray area 51 along twoadjacent edges of said lower mold member 50. A plurality of positivehexagonal standoffs 52 are disposed on the upper face of lower moldmember 50. Said hexagonal standoffs 52 are of roughly uniform height andpatterned to form interconnected interstitial channels 53 in acontinuous desired pattern. In the preferred embodiment, saidinterconnected interstitial channels are in the form of hexagonalhoneycombs. Standoffs 54 are disposed at desired intervals within sunkentray area 51. Although positive hexagonal standoffs 52 can beconstructed of different materials and mechanically or otherwise affixedto the upper surface of said lower mold member, it is contemplated inthe preferred embodiment that said lower mold member be constructed froma single source material, such as aluminum or the like, wherein saidhexagonal standoffs and associated interstitial channels are machinedfrom said source material. Lower mold member 50 also includes raisedperipheral retaining walls 55, as well as peripheral handling ledge 56.Peripheral retaining walls 55 and handling edge 56 extend around theouter peripheral edges of lower mold member 50.

[0050]FIG. 6 depicts a cross sectional view of lower mold member 50taken substantially along line 6-6 of FIG. 5. As can be seen, lower moldmember 50 contains sunken tray area 51. Standoff 54 is disposed withinsunken tray area 51. Adjacent to said sunken tray area 51 are aplurality of positive hexagonal standoffs 52, as well as interstitialchannels 53 disposed between said positive hexagonal standoffs. Itshould be noted that upper surfaces of said positive hexagonal standoffs52 are of uniform height and level relative to one another. Furthermore,raised retaining walls 55 extends to a greater height than the uppersurface of said positive hexagonal standoffs 52. In the preferredembodiment, interstitial channels 53 are of uniform depth.

[0051]FIG. 7 depicts upper mold member 70, which is a roughlyrectangular panel constructed of a material which is compatible withlower mold member 50. Upper mold member 70 is sized to be receivedwithin fairly close tolerance inside raised peripheral retaining walls55 of lower mold member 50. One or more spacing elements 71 are disposedalong the upper surface of upper mold member 70. Said spacing elements71 act to reduce the surface area which is in contact between said uppermold member 70 and an external heat source, such as a platen or hotpress used to elevate the temperature of mold members 50 and 70 duringthe molding process. In the preferred embodiment, spacing elements 71can be of different sizes, and can be located at different locationsalong the upper surface of upper mold member 70 to yield desired heattransfer characteristics.

[0052]FIG. 8 depicts a cross sectional view of upper mold member 70substantially along line 8-8 of FIG. 7. Spacing elements 71 are disposedalong the upper surface of upper mold member 70. Additionally,countersinks 72 are positioned at desired locations along the lowersurface of upper mold member 70.

[0053]FIG. 12 depicts a partial plan view of the lower surface of uppermold member 70 taken substantially along line 12-12 of FIG. 8.Countersinks 72 are positioned along the lower surface of upper moldmember 70. Additionally, recesses 73 can be cut into upper mold member70. Recesses 73, which can be of generally any desired size andconfiguration, create raised elements along the outer surface of panelsmolded using the present invention. Referring to molded panel 30depicted in FIG. 4, said recesses 73 in upper mold member 70 createraised traction promoting elements 38 a on generally planar surface 38.With reference to FIG. 12, said raised traction promoting elements areoriented in a star-like pattern.

[0054]FIG. 13 depicts a cross sectional cut-away of upper mold member 70of the present invention taken substantially along line 13-13 of FIG.12. Upper mold member 70 has countersinks 72 situated on the lowersurface of said upper mold member. Further, recesses 73 are alsodisposed along the lower surface of said upper mold member 70.

[0055] In accordance with the present invention, a method of molding alarge-size panel from thermoplastic resin or other moldable material isprovided as now illustrated with specific reference to panel 30.Referring to FIG. 10, lower mold member 50 is filled with desired typeand amount of thermoplastic resin or other moldable material 60.Although lower mold member 50 can be charged with such resin in a meltedor liquid state, the resin is preferably in solid pellet or granuleform. Such pellets or granules should be sized to permit adequateuniform loading of lower mold member 50, and particularly interstitialchannels 53 thereof. Furthermore, such pellets should ideally be sizedto promote uniform melting, depending upon the particular resin ormoldable material being utilized.

[0056] After filling interconnected interstitial channels 53 of lowermold 50, an additional layer of resin 60 or other moldable material isadded to lower mold member 50. This additional layer 60 of resin orother moldable material forms a nearly uniform topping layer which isdisposed above the upper surface of positive hexagonal standoffs 52, aswell as the resin-filled interstitial channels 53 of lower mold 50, andwhich is held in position by raised peripheral retaining walls 55.Referring to FIG. 11, upper mold member 70 is placed together with lowermold member 50, and received within raised retaining walls 55 of lowermold member 50. Layer 60 of resin or other moldable material is situatedbetween lower mold member 50 and upper mold member 70.

[0057] Thereafter, combined upper and lower mold members are subjectedto elevated heat and pressure. Such heat and pressure must be ofsufficient intensity and duration to cause the thermoplastic resin orother moldable material within said molds to fully melt and uniformlyfill interconnected interstitial channels 53 of lower mold member 50. Assuch, the combined molds are heated to and maintained at a temperatureabove the melt temperature of the particular resin or other moldablematerial being molded.

[0058] After said combined molds have been subjected to sufficient heatand pressure, said molds are then permitted to cool. After cooling, saidupper and lower mold members are separated. Molded panel 30 is in turnseparated from lower mold member 50.

[0059] Although not required, in the preferred embodiment the method ofmanufacturing disclosed herein includes the additional optional step ofapplying pressure to said combined upper mold member 70 and lower moldmember 50 during the cooling phase. Thus, after said combined upper andlower mold members have been subjected to sufficient heat and pressure,said combined molds are permitted to cool under pressure, typicallywithin a separate cold press apparatus. Application of pressure duringthe cooling phase will serve to reduce or alleviate problems associatedwith stress cracking and warping.

[0060] Areas of increased mass defining continuous outer surfaces 34 and35 of large size panel 30 are molded in accordance with the presentinvention by first preparing a molded sacrificial component. FIG. 9depicts such a molded sacrificial component 90. Said molded sacrificialcomponent includes a plurality of open cells 91, as well as cell formingwalls 92. A continuous skin 93 is defined at the base of open cells 91and cell forming walls 92. Although molded sacrificial component 90 canbe separately molded to the desired size and configuration in accordancewith the method of manufacture described herein, or some other method,it should be understood that said molded sacrificial component cansimply be cut down from a larger molded panel such as large-size panel30. In the preferred embodiment, sacrificial components 90 areconstructed of the same material as panel 30 to be molded.

[0061] Prior to loading lower mold member 50 with thermoplastic resin orother moldable material, in the preferred embodiment molded sacrificialcomponent 90 is loaded within one or more of sunken tray areas 51 oflower mold member 50. Thereafter, pelletized resin is added to saidmold, filling upward-facing open cells 91 of molded sacrificialcomponent 90, as well as other portions of lower mold member 50. Themolding process is thereafter carried out as set forth in detail above,resulting in areas of increased mass defining continuous outer surfaces34 and 35 of mat 30 being formed.

[0062] Whereas the invention is herein described with respect to apreferred embodiment, it should be realized that various changes may bemade without departing from essential contribution to the art made bythe teachings hereof.

What is claimed is:
 1. An apparatus for molding panels having cellularstructure comprising: a. a lower pan having a base defining a generallyplanar upper surface, wherein a plurality of roughly vertical channelsextend into said upper surface of said base in a configuration of thedesired cells of said cellular structure; b. retaining walls around theperipheral edges of said lower pan, wherein said retaining walls extendhigher than said generally planar upper surface of said base; and c. alid having roughly planar upper and lower surfaces sized to be receivedwithin said retaining walls around said lower pan.
 2. The apparatusrecited in claim 1, wherein said channels are in the configuration ofhexagonal honeycombs.
 3. A method for manufacturing panels havingcellular structure comprising: a. loading thermoplastic resin or othermoldable material into a lower pan element having a base defining agenerally planar upper surface, wherein a plurality of roughly verticalchannels extend into said upper surface of said base in a configurationof the desired cells of said cellular structure, and having retainingwalls around the peripheral edges of said lower pan, wherein saidretaining walls extend higher than said generally planar upper surfaceof said base; b. placing a lid element having roughly planar upper andlower surfaces on said lower pan within said retaining walls around saidlower pan; c. subjecting the loaded upper and lower elements to elevatedheat and pressure; and d. permitting the loaded upper and lower elementsto cool.
 4. The method of manufacture recited in claim 3, furthercomprising the step of applying elevated pressure during the coolingprocess.
 5. A method of manufacturing a panel having roughly continuousouter surfaces comprising: a. loading a sacrificial molded piece havingcellular structure into a lower hollow pan element; b. loadingthermoplastic resin or other moldable material into said pan over saidsacrificial molded piece; c. placing a lid element having roughly planarupper and lower surfaces on said lower pan element; d. subjecting theloaded upper and lower elements to elevated heat and temperature; and e.permitting the loaded upper and lower elements to cool.
 6. The method ofmanufacture recited in claim 5, further comprising the step of applyingelevated pressure during the cooling process.